The specification details an energy absorbing apparatus which includes one or more longitudinal members. The specification in one embodiment details a guardrail which comprises longitudinal members in the form of rails. For ease of reference, the present invention will now be discussed in relation to a guardrail. Although, it will be appreciated that the present invention may have utility in relation to different energy absorbing applications, utilising telescoping longitudinal members.
Guardrails are widely used throughout the world on the side(s) of highways, motorways and the like to act as a safety barrier to redirect errant vehicles back onto the road. However, the terminal ends of guardrails pose a significant risk to vehicles which have a head on impact therewith. It would therefore be an advantage, if there could be provided a way, in which more of the energy arising from a head on impact with the terminal end of a guardrail, could be absorbed, so as to minimise the damage caused to a vehicle, involved in such a collision.
Current guardrails, marketed as “X-tension” utilise a single set of frangible (shear) bolts to join the second and third rails, and a slider which fits around the first and second rails, at the terminal end of a guardrail, joins the first and second rails together. The slider is bolted to the downstream end of the first rail, and after a head on impact travels along the second rail. When the slider reaches the downstream end of the second rail the upstream end of the second rail impacts with an impact head on the upstream end of the first rail. The shock of this impact with the end of the second rail with the impact head, shears the heads off the shear bolts. As the shear bolts have now failed this disconnects the second and third rails, which can now telescope with respect to one another, as the slider to travels along and gathers the third rail therein, alongside, the first and second rails.
However, once the slider has travelled along the third rail further telescoping with the fourth rail is not possible as a second set of shear bolts cannot be utilised to join the third and fourth rails. As if a second set of shear bolts is used to join the third and fourth rails the applicant has found it is difficult to reliably control the order in which the shear bolts fail. Thus if the downstream second set of shear bolts connecting the third and fourth rails is to fail before the first set of shear bolts upstream this prematurely halts telescoping and energy absorption.
Ideally, it would be desirable if a terminal end of a guardrail could have at least one additional set of shear bolts, connecting downstream rails in a manner that enables more rails to reliably telescope, in sequential order, from upstream to downstream, so as to absorb more energy from a head on impact. However, as mentioned the key is to somehow control when the downstream bolts shear, which is difficult, as the shock of impact automatically transfers force along the rails, and can cause downstream bolts to shear prior to upstream bolts shearing. This, in turn, adversely reduces the capacity of the guardrail to absorb energy.
All references, including any patents or patent applications cited in this specification are hereby incorporated by reference. No admission is made that any reference constitutes prior art. The discussion of the references states what their authors assert, and the applicants reserve the right to challenge the accuracy and pertinency of the cited documents. It will be clearly understood that, although a number of prior art publications are referred to herein, this reference does not constitute an admission that any of these documents form part of the common general knowledge in the art, in New Zealand or in any other country.
Throughout this specification, the word “comprise”, or variations thereof such as “comprises” or “comprising”, will be understood to imply the inclusion of a stated element, integer or step, or group of elements integers or steps, but not the exclusion of any other element, integer or step, or group of elements, integers or steps.
It is an object of the present invention to address the foregoing problems or at least to provide the public with a useful choice.
Further aspects and advantages of the present invention will become apparent from the ensuing description which is given by way of example only.